Catheters have been in use for medical procedures for many years. Catheters can be used for medical procedures to examine, diagnose and treat while positioned at a specific location within the body which is otherwise inaccessible without more invasive procedures. During these procedures a catheter is inserted into a vessel located near the surface of a human body and is guided to a specific location within the body for examination, diagnosis and treatment. For example, one procedure utilizes a catheter to convey an electrical stimulus to a selected location within the human body. Another procedure utilizes a catheter with sensing electrodes to monitor various forms of electrical activity in the human body.
Catheters are used increasingly for medical procedures involving the human heart. Typically, the catheter is inserted in an artery or vein in the leg, neck or arm of the patient and threaded, sometimes with the aid of a guidewire or introducer, through the vessels until a distal tip of the catheter reaches the desired location for the medical procedure in the heart.
A typical human heart includes a right ventricle, a right atrium, a left ventricle and a left atrium. The right atrium is in fluid communication with the superior vena cava and the inferior vena cava. The atrioventricular septum separates the right atrium from the right ventricle. The tricuspid valve contained within the atrioventricular septum provides communication between the right atrium and the right ventricle. On the inner wall of the right atrium, where it is connected with the left atrium, is a thin-walled, recessed portion, the fossa ovalis. Medical procedures are frequently performed in the left atrium using transseptal procedures performed through the interatrial septum. Present in the wall of the left atrium are the entrances to the four pulmonary veins: the right superior, the left superior, right inferior and left inferior pulmonary veins. The mitral valve contained in the atrioventricular septum provides communication between the left atrium and the left ventricle.
In the normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electro-chemical signals pass sequentially through the myocardium from the sinoatrial (SA) node to the atrioventricular (AV) node and then along a well defined route which includes the His-Purkinje system into the left and right ventricles.
Sometimes abnormal rhythms occur in the heart which are referred to generally as arrhythmia. Abnormal arrhythmias which occur in the atria are referred to as atrial arrhythmia. Three of the most common atrial arrhythmia are ectopic atrial tachycardia, atrial fibrillation and atrial flutter. Atrial fibrillation is the most common of all sustained cardiac arrhythmias. While it is present in less than one percent of the general population, it has been estimated that at least 10 percent of the population over 60 is subject to atrial fibrillation. Although frequently considered to be an innocuous arrhythmia, atrial fibrillation can result in significant patient discomfort and even death because of a number of associated problems, including: an irregular heart rate which causes patient discomfort and anxiety, loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure, and stasis of blood flow, which increases the likelihood of thromboembolism.
Efforts to alleviate these problems in the past have included significant usage of pharmacological treatments. While pharmacological treatments are sometimes effective, in some circumstances drug therapy has had only limited effectiveness and is frequently plagued with side effects, such as dizziness, nausea, vision problems and other difficulties.
An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia is catheter ablation. The use of catheters for ablating specific locations within the heart has been disclosed, for example in U.S. Pat. Nos. 4,641,649, 5,263,493, 5,231,995, 5,228,442 and 5,281,217.
The use of RF energy with an ablation catheter contained within a transseptal sheath for the treatment of W-P-W in the left atrium is disclosed in Swartz, J. F. et al. "Radiofrequency Endocardial Catheter Ablation of Accessory Atrioventricular Pathway Atrial Insertion Sites" Circulation Vol. 87, pgs. 487-499 (1993).
Ablation of a specific location within the heart requires the precise placement of the ablation catheter within the heart. One procedure used to place ablation catheters at a specific location in the heart utilizes a guiding introducer or a pair of guiding introducers. Ablation procedures using guiding introducers for treatment of atrial arrhythmia have been disclosed in U.S. Pat. Nos. 5,497,774, 5,427,119, 5,575,166, 5,640,955, 5,564,440 and 5,628,316. Lesions are produced in the heart tissue as an element of these procedures.
Placement of catheters at particular locations in a human body is sometimes accomplished using guide wires. For example, U.S. Pat. No. 5,163,911 discloses a catheter system utilizing a guidewire to guide a working catheter within the vasculature to perform medical procedures. U.S. Pat. No. 5,209,730 discloses an over-the-wire balloon dilation catheter for use within a vessel of the heart. A similar extendable balloon on a wire catheter system is disclosed in U.S. Pat. No. 5,338,301.
A different type of ablation catheter is disclosed in U.S. Pat. No. 5,482,037, which discloses an electrode catheter for insertion into a cavity of the heart. U.S. Pat. Nos. 5,487,385 and 5,575,810 disclose ablation systems which are utilized for mapping and ablation procedures within the right atria of the heart.
Conventional ablation procedures utilize a single distal electrode secured to the tip of an ablation catheter. Increasingly, however, cardiac ablation procedures utilize multiple electrodes affixed to the catheter body.
The ablation catheters commonly used to perform these ablation procedures produce scar tissue at particular points in the cardiac tissue by physical contact of the cardiac tissue with an electrode of the ablation catheter. One difficulty in obtaining an adequate ablation lesion using conventional ablation catheters is the constant movement of the heart, especially when there is an erratic or irregular heart beat. Another difficulty in obtaining an adequate ablation lesion is caused by the inability of conventional catheters to obtain and retain uniform contact with the cardiac tissue across the entire length of the ablation electrode surface. Without such continuous and uniform contact, any ablation lesions formed may not be adequate.
Effective ablation procedures are sometimes quite difficult because of the need for an extended linear lesion, sometimes as long as about 3 inches to 5 inches (approximately 8 cm. to 12 cm.). To produce such a linear lesion of this length within an erratically beating heart is a difficult task.
One process for the production of linear lesions in the heart by use of an ablation catheter is disclosed in U.S. Pat. Nos. 5,487,385, 5,582,609 and 5,676,662. In addition, a process for the production of a series of linear lesions in the atria for the treatment of atrial arrhythmia is disclosed in U.S. Pat. No. 5,575,766.
To form linear lesions within the heart using a conventional ablation tip electrode requires the utilization of procedures such as a "drag burn". During this procedure, while ablating energy is supplied to the ablating electrode, the ablating electrode is drawn across the tissue to be ablated, producing a line of ablation. Alternatively, a series of points of ablation are formed in a line created by moving the ablating electrode incremental distances across the cardiac tissue. The effectiveness of these procedures depends on a number of variables including the position and contact pressure of the ablating electrode of the ablation catheter against the cardiac tissue, the time that the ablating electrode of the ablation catheter is placed against the tissue, the amount of coagulum that is generated as a result of heat generated during the ablation procedure and other variables associated with a beating heart, especially an erratically beating heart. Unless an uninterrupted track of ablated cardiac tissue is created, unablated cardiac tissue or incompletely ablated cardiac tissue may remain electrically active, permitting the continuation of the reentry circuit which causes the arrhythmia. Thus, new devices are necessary for the production of linear lesions in the heart.